Hot stretch sheet forming of certain high elongation aluminum alloys has been used to make one-piece body panels for automotive vehicles.
Cold rolled sheets of fine-grain magnesium and manganese containing alloys are heated to a forming temperature in the range of, for example, 400 to 510° C. and stretch formed against a heated forming tool surface into the shape of the panel. A sheet blank is gripped at its edges between the forming surface tool on one side of the sheet and an opposing tool defining a pressure chamber on the other side of the blank. A pressurized working gas is admitted into the chamber stretching and draping the heat softened sheet into compliance with the forming surface. After forming, the pressurized gas is released, the hot tools are parted, and the formed hot sheet product carefully removed from the forming tool to a cooling rack.
The sheet metal blanks are typically about one to three millimeters thick and there is some localized thinning of the sheet material during the stretch forming process. In applications involving the forming of automobile body panels, the original blanks are often generally rectangular with sides three or four feet in length. When a passenger compartment floor pan for a vehicle is to be stretched formed, the blank is considerably larger.
Sometimes a panel design requires reinforcement pieces to be attached at specific locations on a side of the one-piece panel. Such reinforcing pieces are often considerably smaller than the panel to which they are to be attached. These reinforcement sheet pieces may provide local thickening for structural support or for attachments or the like. They have been formed separately and welded or otherwise suitably attached to the formed panel during final assembly. It would be desirable to form the reinforcement pieces when the main panel is being stretch formed so that the reinforcement precisely fits the formed part. However, it is necessary to suitably position reinforcing sheet pieces on the relatively large area tool for forming the hot sheet blank. When a number of parts are being produced successively the forming tool is hot and the reinforcing piece must be positioned on a hot forming surface of the tool.
Accordingly, it is an object of this invention to provide a practice for locating pieces, sometimes relatively small pieces, of sheet metal on a forming tool before a sheet metal blank is gripped over the tool surface for hot stretch forming into a body panel or the like.